Roller (or peristaltic) pumps have many uses in the medical field. For example, roller pumps are used during cardiovascular surgery to facilitate circulation of blood between a patient and a heart-lung machine. Other common medical uses are the transfer of blood between a patient and a kidney dialyzer, and intravenous (IV) feeding of IV solutions. Generally, roller pumps are simply structured, generate a constant flow, and use disposable tubing through which a fluid medium is transferred.
Roller pumps generally comprise a pump drive and a pump head. The pump drive is a unit that drives or causes rotation in the pump head in order for the roller pump to pump a fluid medium. The pump head comprises a pump stator and a pump rotor. The pump stator is essentially a chamber or housing having an inner circumferential surface against which one or more tubes are compressed by the pump rotor. The pump rotor, which is rotatable, is arranged in the pump stator in such a manner that the pump rotor engages tubing positioned in the pump stator with one or more rollers. Upon rotation of the pump rotor by a rotating shaft that is part of the pump drive, the rollers compress the tubing against the inner circumferential surface of the pump stator as they are rolled along the tubing. The fluid medium contained in the tubing is then transported in a direction of the pump rotor rotation.
It is important that roller pumps be adjustable. One way that roller pumps are generally adjustable is with regard to the rate of rotation of the rotor, including the rollers. The rate of rotation affects the amount of fluid medium that may be transferred by the pump. The rate of rotation of the rollers is generally adjusted using controls on the pump or the system in which the pump is integrated.
Another way that roller pumps are generally adjustable is with regard to the distance between the rollers. There are a couple of reasons that the distance between the rollers may be varied. First, the distance between the rollers may be varied to change the amount that the rollers occlude or compress the diameter of the tubing in the pump as they move, which affects the pumping rate. The amount of occlusion of the tubing also affects the amount of suction on the fluid medium by the roller pump. If the roller pump is used in certain portions of the anatomy, there may be limits on the amount of suction that may be applied safely to withdraw a fluid medium. An example of such a use for a roller pump is connected to a heart vent line, where too much suction could result in tissue damage.
Second, the distance between the rollers may be adjusted to allow for tubing having different sizes or qualities to be used in a roller pump. Tubing that is commonly used in roller pumps is extruded tubing. As a result of its production, such tubing has variations in wall thickness as well as in overall inner and outer diameters. These variations can be enough to change a typical calibration of a roller pump rotor to be under occlusive or over occlusive. As a result, the pump rate may change from the desired rate. In addition, variations in occlusion may cause harm to the fluid being pumped (e.g., blood) or to the tubing itself, thereby causing risk of tubing spallation or even rupture.
Some prior art roller pumps do not allow adjustment of the distance between the rollers, and have the distance between the rollers set during manufacture. If, however, a roller pump does provide a mechanism for manually adjusting the distance between the roller and the inner circumferential surface of the pump stator (i.e., adjusting the length of the roller arms), often the adjustments are inefficient to perform in the surgical field because they have to be followed by a time intensive calibration process of the pump.
As an alternative to adjusting the distance between the rollers on a rotor, in some roller pumps, the rotor may be removed and replaced with a rotor applicable for a different size of tubing or amount of occlusion. The process of changing out such a rotor is time intensive and may also require calibration of the pump.